Movement of the tympanic membrane produces a sound pressure in the middle ear that is transmitted to the oval and round windows. Acoustic coupling is due to the difference in sound pressures acting on these areas. The pressure at each window is different because of the small distance between windows and the different orientation of each window relative to the tympanic membrane. In normal ears, the difference in pressures between the oval and round windows (acoustic coupling) is negligible.
In some diseased and reconstructed ears, the difference becomes significant and can greatly affect hearing. Specifically, when the ossicular chain is interrupted or absent, shielding of the round win dow results in redirection of all sound energy into the oval window.9 When this is performed, acoustic coupling plays a significant role in sound pressure conduction for cochlear stimulation.
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